Method and composition for removing uremic toxins in dialysis processes

ABSTRACT

Methods and devices for providing dialysis treatment are provided. The device includes a resin bed including zirconium phosphate, zirconium oxide, and urease.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/774,359, filed Jul. 6, 2007, which is a divisional of U.S. patentapplication Ser. No. 09/990,673, filed Nov. 13, 2001, now issued as U.S.Pat. No. 7,241,272, the entire contents of which are expresslyincorporated herein by reference.

BACKGROUND

The present invention relates generally to methods of treatment. Morespecifically, the present invention relates to dialysis processes.

Due to disease or insult or other causes, the renal system can fail. Inrenal failure of any cause, there are several physiologicalderangements. The balance of water, minerals (Na, K, Cl, Ca, P, Mg, SO₄)and the excretion of daily metabolic load of fixed hydrogen ions is nolonger possible in renal failure. During renal failure, toxic endproducts of nitrogen metabolism (urea, creatinine, uric acid, andothers) can accumulate in blood and tissues.

Dialysis processes have been devised for the separation of elements in asolution by diffusion across a semi-permeable membrane (diffusive solutetransport) down a concentration gradient. Principally, dialysiscomprises two methods: hemodialysis and peritoneal dialysis.

Hemodialysis treatment utilizes the patient's blood to remove waste,toxins, and excess water from the patient. The patient is connected to ahemodialysis machine and the patient's blood is pumped through themachine. Catheters are inserted into the patient's veins and arteries toconnect the blood flow to and from the hemodialysis machine. Waste,toxins, and excess water are removed from the patient's blood and theblood is infused back into the patient. Hemodialysis treatments lastseveral hours and are generally performed in a treatment center aboutthree or four times per week.

Peritoneal dialysis utilizes a dialysis solution and dialysate, which isinfused into a patient's peritoneal cavity. The dialysate contacts thepatient's peritoneal membrane in the peritoneal cavity. Waste, toxins,and excess water pass from the patient's bloodstream through theperitoneal membrane and into the dialysate. The transfer of waste,toxins, and water from the bloodstream into the dialysate occurs due todiffusion and osmosis. The spent dialysate is drained from the patient'speritoneal cavity to remove the waste, toxins, and water from thepatient.

There are various types of peritoneal dialysis, including continuousambulatory peritoneal dialysis (CAPD) and automated peritoneal dialysis(APD). CAPD is a manual dialysis treatment in which the patient connectsan implanted catheter to a drain and allows a spent dialysate fluid todrain from the peritoneal cavity. The patient then connects to a bag offresh dialysate and manually infuses the fresh dialysate through thecatheter and into the patient's peritoneal cavity. The patientdisconnects the catheter from the fresh dialysate bag and allows thedialysate to dwell within the cavity to transfer waste, toxins, andexcess water from the patient's bloodstream to the dialysate solution.After the dwell period, the patient repeats the manual dialysisprocedure.

In CAPD the patient performs several drain, fill, and dwell cyclesduring the day, for example, about four times per day. Each treatmentcycle typically takes about 3-4 hours. Manual peritoneal dialysisperformed by the patient requires a great deal of time and effort by thepatient. The patient is routinely inconvenienced leaving ampleopportunity for therapy enhancements to improve patient quality of life.

Automated peritoneal dialysis is similar to continuous peritonealdialysis in that the dialysis treatment includes a drain, fill, anddwell cycle. However, a dialysis machine automatically performs 3-4cycles of peritoneal dialysis treatment, typically overnight while thepatient sleeps.

To this end, a dialysis machine is fluidly connected to an implantedcatheter. The dialysis machine is also fluidly connected to a source offresh dialysate, such as a bag of dialysate solution, and to a fluiddrain. The dialysis machine pumps spent dialysate from the peritonealcavity though the catheter to the drain. Then, the dialysis machinepumps fresh dialysate from the dialysate source through the catheter andinto the patient's peritoneal cavity. The dialysis machine allows thedialysate to dwell within the cavity to transfer waste, toxins, andexcess water from the patient's bloodstream to the dialysate solution.The dialysis machine is computer controlled so that the dialysistreatment occurs automatically when the patient is connected to thedialysis machine, for example, overnight.

Several drain, fill, and dwell cycles will occur during the treatment.Also, a last fill is typically used at the end of the automated dialysistreatment so that the patient can disconnect from the dialysis machineand continue daily functions while dialysate remains in the peritonealcavity. Automated peritoneal dialysis frees the patient from manuallyperforming the drain, dwell, and fill steps, and can improve thepatient's dialysis treatment and quality of life.

In view of recent developments and therapies, the line betweentraditional peritoneal dialysis and hemodialysis has become blurred. Forexample, some therapies use components of both therapies.

A recent therapy is regenerative dialysis. In this system a dialysissystem is used that includes a cartridge for dialysate regeneration. Thecartridge includes a resin bed including zirconium-based resins. Anexample of a cartridge that is used in such a system is manufacturedunder the name Redy by Sorb Technology, Oklahoma City, Okla. Thissystem, however, requires the constant attention of medical personnel.Moreover, the dialysate that is regenerated by the cartridge has anundesirable sodium and pH level. In this regard, the dialysis solutiondoes not have a physiologic pH or electrolyte content. This isespecially a problem if the dialysis solution is to be reinfused intothe peritoneal cavity of a patient.

SUMMARY

The present invention provides improved systems as well as methods forproviding dialysis to a patient. More specifically, in an embodiment,the present invention provides systems, cartridges, and methods forregenerative dialysis therapies. However, it should be noted that thecartridge of the present invention can be used in a variety of therapiesincluding hemodialysis and peritoneal dialysis therapies as well asacute dialysis.

To this end, in an embodiment, a device for removing uremic toxins in adialysis procedure is provided comprising a body having an inlet and anoutlet and defining an interior, the interior including a layercomprising urease, a layer comprising zirconium oxide, a layercomprising zirconium phosphate, and a layer comprising carbon, and thedevice being so constructed and arranged so that a fluid entering thedevice contacts the zirconium oxide layer upon entering the devicebefore contacting the urease or the zirconium phosphate layer.

In an embodiment, the zirconium oxide is in bicarbonate form.

In an embodiment, the zirconium oxide is in hydroxyl form.

In an embodiment, the carbon layer is located in juxtaposition to theoutlet.

In an embodiment, the fluid flows through a layer of zirconium oxidebefore entering the carbon layer.

In an embodiment, the zirconium phosphate has a pH of approximately 2 toabout 8.

In an embodiment, the zirconium oxide has a pH of approximately 6 toabout 13.

In an embodiment, two separate layers of zirconium phosphate areprovided.

In an embodiment, two separate layers of zirconium oxide are provided.

In an embodiment, open headers at each of the inlet and outlet end ofthe device are provided.

In an embodiment, an opening for venting a gas to the atmosphere locatedat the outlet end is provided.

In an embodiment the urease layer is the first layer.

In an embodiment the zirconium phosphate layer is located before thezirconium oxide layer.

In a further embodiment of the present invention, a cartridge for use ina dialysis system for removing toxins is provided comprising a bodyhaving an inlet end and an outlet end. The body includes an interiorincluding at least four layers, the layers including a first layer of aresin selected from the group consisting of zirconium phosphate having apH of approximately 2.5 to about 5 and urease, a second layer of a resinselected from the group consisting of zirconium oxide having a pH ofapproximately 9 to about 13 and urease, a third layer of zirconiumphosphate, and a fourth layer of zirconium oxide having a pH ofapproximately 6.5 to about 7.5. The interior is so constructed andarranged that a fluid entering the interior from the first inlet endflows through the first layer, then the second layer, then the thirdlayer, and then the fourth layer.

In an embodiment, the first layer comprises approximately 200 to about800 grams of zirconium phosphate.

In an embodiment, the fourth layer comprises approximately 50 to about200 grams of carbon.

In an embodiment, the urease is a cross-linked enzyme.

In yet another embodiment, a device for regenerating a dialysis solutionis provided. The device includes a body including a resin bed. The resinbed includes at least a layer of urease, zirconium phosphate, zirconiumoxide, and carbon and being so constructed and arranged that a dialysissolution having a pH that is either basic or acidic will exit thecartridge after it passes through the resin bed at a pH of approximately7 to about 7.8.

In an embodiment, the first layer of the resin bed that the solutioncontacts is selected from the group consisting of zirconium phosphatehaving a pH of approximately 2.0 to about 5 and urease.

In an embodiment, the second layer that the solution passes through inthe resin bed is selected from the group consisting of zirconium oxidehaving a pH of approximately 9 to about 13 and urease.

In an embodiment, the third layer of the resin bed that the solutionpasses through is zirconium phosphate.

In an embodiment, the fourth layer of the cartridge that the solutionpasses through is zirconium oxide having a pH of approximately 6.8 toabout 7.5.

In an embodiment, the pH of the solution exiting the cartridge isapproximately 7.4.

In a further embodiment, a device for use in a system for treating apatient with a dialysis solution is provided. The device including aninlet in fluid communication with a source of dialysis solution, a bodyincluding the inlet and defining an interior and having an outlet, andthe body including a resin bed including a layer of urease, a layer ofzirconium oxide, and a layer of zirconium phosphate that define a threelayer structure. The resin bed is oriented so that the first layer thatthe dialysis solution contacts of the three layer structure is eitherthe urease or the zirconium phosphate layer and the zirconium oxidelayer is so constructed and arranged that a basic or an acidic dialysissolution entering the inlet will exit the outlet with a physiologicallyacceptable pH.

In an embodiment, the device is used in a regenerative dialysis system.

Still further, in an embodiment, a method for constructing a cartridgefor use in a system for providing dialysis is provided. The methodcomprising the steps of providing a resin bed including zirconium oxideand zirconium phosphate and selecting and orienting the zirconium oxideand zirconium phosphate to allow the cartridge to remove uremic toxinspresent in a dialysis solution entering the resin bed and causing thedialysis solution exiting the cartridge to be at a physiological pH andinclude a physiological electrolyte balance.

In an embodiment, the method includes the steps of providing a bodyhaving an inlet and an outlet and defining an interior, the interiorincluding a layer comprising urease, a layer comprising zirconium oxide,a layer comprising zirconium phosphate, and a layer comprising carbon;and the device being so constructed and arranged so that a fluidentering the device contacts the zirconium phosphate layer upon enteringthe device before contacting the urease on the zirconium oxide layer.

In a yet further embodiment, a method for providing dialysis is providedcomprising the steps of removing uremic toxins by passing a dialysisfluid through a body having an inlet and an outlet and defining aninterior, the interior including at least four layers, a first layercomprising either zirconium phosphate having a pH of approximately 2.5to about 5 or urease, a second layer comprising either zirconium oxidehaving a pH of approximately 9 to about 13 or urease, a third layercomprising zirconium phosphate and a fourth layer comprising zirconiumoxide having a pH of approximately 6.8 to about 7.5.

Additionally, in an embodiment, a method of providing regenerativedialysis is provided comprising the step of removing uremic toxins bypassing a dialysis fluid through a body having an inlet and an outletand defining an interior, the interior including at least four layers, afirst layer comprising either zirconium phosphate having a pH ofapproximately 2.5 to about 5 or urease, a second layer comprising eitherzirconium oxide having a pH of approximately 9 to about 13 or urease, athird layer comprising zirconium phosphate and a fourth layer comprisingzirconium oxide having a pH of approximately 6.8 to about 7.5.

An advantage of the present invention is to provide an improved dialysisprocedure.

Moreover, an advantage of the present invention is to provide animproved cartridge for removing impurities from a dialysis fluid.

Still, an advantage of the present invention is to provide an improvedsystem for providing dialysis.

Further, an advantage of the present invention is to provide an improvedcartridge that can be used in a single loop or multiple loop system.

Additionally, an advantage of the present invention is to provide animproved resin bed for a cartridge for a dialysis system.

Additionally, an advantage of the present invention is to provide animproved cartridge that is constructed and arranged so that dialysissolution that exits the cartridge has a physiological pH and electrolytecontent.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates schematically a system for performing dialysispursuant to the present invention.

FIG. 2 illustrates a cross-sectional view of an embodiment of thecartridge of the present invention.

FIG. 3 illustrates graphically ammonium effluent concentration (ppm)versus mass ammonium delivered (mEq) for zirconium phosphate availablefrom two suppliers (Sorb technologies and magnesium elektron).

FIG. 4 illustrates graphically sodium capacity as a function ofzirconium oxide pH.

FIG. 5 illustrates an embodiment of a cross-sectional view of a resinbed of a cartridge of the present invention.

FIG. 6 illustrates a further embodiment of a resin bed of a cartridge ofthe present invention.

FIG. 7 illustrates a still further embodiment of a resin bed of acartridge of the present invention.

FIGS. 8-10 illustrate graphically the results of Experiment No. 2.

FIG. 11 illustrates the system that was used in Experiment No. 3 fortesting the cartridges of the present invention.

FIG. 12 illustrates a cross-sectional view of the layers of thecartridge used in Experiment No. 3.

FIGS. 13 a-c illustrate pH, sodium bicarbonate profiles of samples takenpursuant to Experiment No. 1.

FIGS. 14 a-c represent pH, sodium bicarbonate profiles of samples takenpursuant to Experiment No. 1.

FIGS. 15 a-c illustrate pH bicarbonate and sodium profiles of samplesover time pursuant to Experiment No. 1.

FIG. 15 d illustrates the urea conversion over time pursuant toExperiment No. 1.

DETAILED DESCRIPTION

The present invention relates to methods of providing dialysistreatment. Additionally, the present invention relates to systems forproviding dialysis. More specifically, in an embodiment, the presentinvention provides improved cartridges that are used to remove uremictoxins.

In a preferred embodiment, the present invention relates to systems andcomponents for use in continuous flow peritoneal dialysis procedure.However, it should be noted that the present invention can be used in avariety of methods for providing dialysis including hemodialysis andperitoneal dialysis

Continuous flow peritoneal dialysis is achieved by continuously infusinginto and draining from the peritoneum a solution. For example, a closedloop or recirculating dialysis can be used where the solution iscontinuously recirculated to the patient. This can have the advantage ofsubstantially reducing the amount of solution needed for a treatment.However, it is necessary to regenerate the solution with the exactglucose and electrolyte requirements required by the patient. Thistherapy is designed to be performed primarily at night.

Generally, the system comprises a disposable set including a pumpcassette, cartridge, dialyzer, and solution concentrate. FIG. 1illustrates generally a schematic of the system 10 for providingdialysis treatment pursuant to the present invention.

As illustrated in FIG. 1, two loops are provided: a patient loop 11; anda regeneration loop 12. However, it should be noted that the presentinvention can be used in a system including only one loop or more thantwo loops. The patient loop 11 is used to dialyze the patient 14 withdialysate. The regeneration loop 12 is used to regenerate the dialysate.As illustrated generally, the dialysate is pumped from a bag 16 in thepatient loop 11 into the patient 14 through a catheter 24. Spent fluidis then fed from the patient 14 back into the dialyzer 20.

A variety of components can be used in the patient loop. In a preferredembodiment a dual lumen catheter 24 is used. The dual lumen catheterprovides for continuous, flow in to and out of the peritoneal cavity ofthe patient. To this end, the dual lumen catheter is implanted in thepatient. An example of a catheter for use in the system 10 of thepresent invention is disclosed in U.S. patent application Ser. No.09/689,508, filed on Oct. 12, 2000, and entitled “Peritoneal DialysisCatheter,” the disclosure of which is incorporated herein by reference.However, it should be noted that two single lumen catheters can be usedas well as a single lumen catheter.

To regenerate the dialysate, the regeneration loop 12 is provided. Inthe embodiment illustrated, the regeneration loop 12 preferably includesconcentrate in a container 26, a cartridge 32, an ultrafiltrate (UF)pump, and a UF collection means that communicates with the patient loop11 via the dialyzer 20. A concentrate pump is provided to pump theconcentrate 26 from the container through fluid path 27. The fluid inthe regeneration loop is pumped through the dialyzer 20 in a countercurrent fashion to the fluid in the patient loop 11.

The dialyzer 20 is provided to remove water and small solutes such asurea, and creatinine from spent dialysate in the patient loop 11. Thedialyzer 20 provides a sterile independent barrier between the patientloop 11 and the regeneration loop 12. Any dialyzer 20 can be used thatprovides a high clearance of small molecules across the dialyzer. Uricacid will diffuse across the dialyzer, ultrafiltrate is also removed.

It should be noted that although the cartridge 32 of the presentinvention is illustrated as being used in a two loop system, it can beused in other systems. For example, it is envisioned that the cartridgecan be used in a one loop system.

Referring now to FIG. 2, a cross-sectional view of an embodiment of thecartridge 32 of the present invention is illustrated. The cartridge 32includes a resin bed 34 that is designed to modify the chemistry of therecirculating dialysate and remove uremic toxins. At the same time,pursuant to the present invention, the cartridge 32 maintainselectrolyte concentrations and the solution pH of the dialysate atphysiologic levels.

The cartridge 32 generally comprises: a main body 40, an inlet cap 42,the resin bed 34, and an outlet cap 44. In the embodiment illustrated,fluid is routed into the cartridge 32 through the inlet cap 42 that islocated at a bottom 46 of the cartridge 32. In the embodimentillustrated, a small open header chamber 48 prior to the resin bed 34 isused to distribute the flow of fluid evenly across the cross-section ofthe cartridge 32 and thereby the resin bed 34. The fluid preferablyflows upwardly through the resin bed 34.

In the embodiment illustrated, downstream of the final section of theresin bed 34 there is located another open header chamber 50. The secondopen header chamber 50 is located before a gas separation chamber 52.The second header chamber 50 is used to maintain an even fluid velocitydistribution throughout the resin bed 34.

The liquid level in the gas separation chamber 52 is maintained within aspecified range to provide an air space above the liquid in thecartridge 32. Gases that are produced during therapy, e.g., carbondioxide, are vented from the cartridge 32 to the environment through apassage 54 on the outlet cap 44. If desired, this passage 54 may includea filter member. A submerged, or partially submerged, barrier in the gasseparation chamber 52 produces a flow pattern that restricts gases frombeing drawn to the liquid outlet.

At the outlet cap 44 of the cartridge 32 the liquid outlet port 58 islocated. The liquid outlet 58 port removes liquid from the chamber ofthe cartridge 32 through the outlet cap 44 using a siphon action. Ifdesired, an additional port may be used to add a chemical concentrate tothe volume of liquid in the gas separation chamber to reconstitute thechemical composition of the fluid outflow.

In an embodiment, the interior of the cartridge 32 has a rough surface.The rough surface is designed so that it prevents fluid from flowingalong the sides of the exterior by passing the resin bed 34.

The resin bed 34, in part, functions to remove waste. In this regard,generally waste is removed using a two-step process. The steps consistof an enzymatic conversion of urea using urease followed by subsequentremoval of the conversion byproducts. In the enzymatic reaction, onemole of urea is decomposed into two moles of ammonia and one mole ofcarbon dioxide. Ammonia (NH₃) is primarily (>95%) present as ammoniumion (NH₄ ⁺), since its pKa of 9.3 is substantially greater than thesolution pH. The carbon dioxide that is formed can either be present asdissolved carbon dioxide or as bicarbonate ion, depending on thesolution pH. Since the pKa for this equilibrium is 6.1, both species maybe present in substantial quantities under conditions of use. Inaddition, if the solution is in communication with a gas phase, thedissolved carbon dioxide is in equilibrium with the carbon dioxidepresent in the gas phase.

The resin bed includes at least four layers, although more layers can beused. Generally, the layers of the resin bed comprise at least: a ureaselayer; a layer of zirconium phosphate; a layer of zirconium oxide; and alayer of carbon.

The purpose of the urease layer is to enzymatically convert urea that ispresent in the solution that is flowing through the resin bed 34 toammonia and carbon dioxide. In solution, ammonia acts as a base sincethe formation of ammonium results from the donation of H⁺. Similarlycarbon dioxide (CO₂) acts as an acid, since the formation of bicarbonate(HCO₃) donates H+ to solution. The net result of the urease reaction isto increase the pH.

In an embodiment, 25 to 250 mg of urease are used, although any amountof urease can be used that is sufficient to convert the urea present inthe solution to ammonia and carbon dioxide. Preferably, urease comprisesthe first or second layer of the resin bed.

A variety of urease materials can be used. For example, crosslinkedenzyme crystals of urease (Urease-CLEC) can be used. This material isultra pure and has high specific activity. Therefore, a very smallquantity of this urease is sufficient to provide the desiredurea-conversions.

By way of example, the amount of urease-CLEC required was optimized fortwo different internal diameters of the cartridge, 31/4″ and 11/4″respectively. Next, in order to determine the optimal contact timebetween urease-CLEC and the substrate stream, the enzyme was blendedwith powdered Zirconium Oxide (ZO). Table 1 shows the optimized amountof urease-CLEC and ZO required to obtain a urea conversion >90%. Thequantity of enzyme used was stable to sterilization with 40 kGyγ-radiation. The flow rate used in all above experiments was 100 ml/min.

TABLE 1 Summary of urease-CLEC required for urea conversion Amount ofColumn urease-CLEC γ- Diameter required Amount of ZO sterilization %Urea (inch) (mg) required (gm) dose (kGy) Conversion 1.25 50 25 >40 903.25 150 150 >40 97

For this particular approach of using urease-CLEC, the primary challengeis in the development of procedures for blending very small quantitiesof urease-CLEC with large quantities of ZO. Where as, the small quantityis advantageous for easy containment within the polymer matrix of anultrafiltration membrane. The use of these urease-impregnatedultrafiltration membranes provide several benefits over the currentlyavailable methods:

1) Better urease containment.

2) Reduced cartridge size resulting in enhanced ease of use by patient.

3) Ease of use during cartridge manufacture

4) Increased safety over the existing system (due to better containmentof urease in the cartridge)

Table 2 shows the urea conversion observed at various flow rates using aurease-CLEC impregnated membrane. The membrane tested had a diameter of1 inch, thus, the flow rates used were 1.3, 2.7 and 5.3 ml/min, whichcorrespond to a flux of 50, 100 and 200 ml/min through a 3.25 inchmembrane.

TABLE 2 Sample results obtained from a γ-sterilized urease-CLEC-impregnated membrane Amount of γ- Urease-CLEC Membrane Flow ratesterilization % Urea (mg) diameter (inch) (ml/min) dose (kGy) Conversion15.85 1 1.3 40 87.3 15.85 1 2.7 40 79.2 15.85 1 5.3 40 66.9

Although, the urea conversions observed are lower than required, betterconversions can be expected from membranes prepared with largerquantities of urease-CLEC. Additionally by employing two membranes ineach cartridge a higher overall urea conversion can be obtained.

By way of further example, alumina-stabilized urease can also be used.Upon wetting, the urease dissolves but, it is immediately absorbed bythe alumina particles that are located in close proximity. The endresult is urease that is physically absorbed by the alumina in closeproximity. This urease exposed to γ-irradiation at a dose of 15 kGy inthe presence of γ-irradiation retained 75% of its initial activity.

Referring now to the zirconium phosphate layer, zirconium phosphate canabsorb, under certain conditions, ammonium ion, calcium, magnesium, andsodium. Ammonium ion is removed from solution via an ion exchangeprocess using zirconium phosphate. Zirconium phosphate contains twocounter-ions—hydrogen (H⁺) and sodium (Na⁺). Release of the counter-ionsis determined by the solution pH and the current loading state of theresin. In addition to its role as an ion exchange resin, zirconiumphosphate also has a considerable buffering capacity.

If the loading state pH of the resin is 6.2 then when in contact with an(acidic) solution having a pH of less than 6.2, the resin will releaseNa⁺ in exchange for H⁺, even in the absence of any other ions. Incontact with a (basic) solution having a pH of greater than 6.2, theresin will release H⁺ in exchange for Na⁺, even in the presence of othercations. In contact with a solution having a pH of 6.2 and containingammonium, the resin will exchange a mixture of Na⁺ and H⁺ ions for NH₄ ⁺such that its equilibrated pH remains unchanged. The zirconium phosphateresin possesses excellent capacity for ammonium, and this capacity isunaffected by changes in equilibrated pH within a given range (pH6.0-7.2). The desired pH of the zirconium phosphate will depend, inpart, on its location in the resin bed, e.g., the component it isdesigned to remove. To this end, the zirconium phosphate layer can havea pH of between approximately 2 to about 8. Preferably, zirconiumphosphate is present in a range of approximately 200 to about 800 grams.The amount of zirconium phosphate necessary is at a minimum that amountthat is sufficient to remove the ammonium that is generated. The levelof ammonium generated is determined by the urea that is to be removed bythe cartridge. Thus, the amount of zirconium phosphate equals theammonium to be removed divided by the capacity of the zirconiumphosphate, to remove ammonium, which can be determined experimentally.

For example, a process for determining the quantity of zirconiumphosphate required in the device can be determined as follows.Equilibrium data is employed to make a first pass guess at the amount ofzirconium phosphate required. For a given cartridge containing aparticular amount of zirconium phosphate, the effluent ammoniumconcentration profile is obtained. The capacity of a given cartridge isdefined as the mass of ammonium delivered at the time that the effluentconcentration exceeds a prescribed level. In an embodiment, thiseffluent cutoff level is set at 20 ppm. For example, in the data fromFIG. 3, for a small prototype device, the ammonium capacity isapproximately 4.2 mEq for 10.5 g zirconium phosphate, an inputconcentration of 3.9 mEq/L ammonium, and a bulk flow rate of 8.3 mL/min(breakthrough at the 20 ppm level occurs after absorption of 4.2 mEqammonium).

In an embodiment, it is believed that the quantity of zirconiumphosphate required is on the order of approximately 600 to about 800 g.In an embodiment, zirconium phosphate will comprise more than half ofthe cartridge by weight. As to its location in the resin bed, preferablyzirconium phosphate can comprise the first layer through all but thelast layer of the resin bed (not including the carbon layer). Moreover,multiple zirconium phosphate layers can be used.

Referring now to the zirconium oxide layer, zirconium oxide resin is anamphoteric resin. This means that the resin's ion exchange propertiesare dependent on the solution pH. If the solution pH is much lower thanthe pI of the resin, the resin acts as an anion exchange resin. If thesolution pH is much greater than the pH of the resin, the resin acts asa cation exchange resin. If the solution pH is near its pI, the resindemonstrates properties of a mixed bed, exchanging both cations andanions. This latter behavior of a mixed bed occurs throughout thephysiologic pH range.

The zirconium oxide layer removes phosphates. The zirconium oxide layer,depending on the pH, can also function to remove sodium. Preferably thezirconium oxide layer has a pH of approximately 6 to about 13.

The phosphate capacity of the resin is very high, thus, the size of thelayer is governed by how much sodium needs to be removed. In likefashion, the amount of zirconium oxide is thereby determined by thecapacity of the zirconium oxide that is used to remove sodium. FIG. 4illustrates graphically the sodium capacity of zirconium oxide as afunction of its pH.

The zirconium oxide layer functions to remove any phosphate that may nothave been absorbed by the other components of the resin bed. Further,the zirconium oxide layer controls the pH of the solution leaving thecartridge. Accordingly, preferably the zirconium oxide layer, if it isthe last layer (not including the carbon layer) of the cartridge 32, hasa pH of approximately 7 to about 9 and in a preferred embodiment,approximately 7.4. Although preferably the zirconium oxide layer is thelast layer (not including the carbon layer), multiple zirconium oxidelayers can be used.

In an embodiment, zirconium oxide is utilized that has been modified byremoving the nitrate ion as the counter ion. In this regard, the nitrateion was exchanged with bicarbonate ion by treating the zirconium oxidewith 15% sodium carbonate solution to a pH of approximately 11.3. Themixture was then washed extensively with water to remove residue sodiumnitrate and sodium carbonate. The resin was then dried under high vacuumat an RT of approximately 24 hours. The resulting resin (0.5 g/mL inwater) at a pH of approximately 8.5, and a conductivity of 155.1 us/cm.The dried resin was further modified by suspending the resin in waterand adding hydrochloric acid until a pH of 7 was achieved. Following thepH adjustment, the resin was washed to remove residual chloride andsodium ions. After each of the washing steps the resin filtrate pH andconductivity was measured. After wash 1, the paper pH was 6.5 to 7 andconductivity 464 us/cm; after wash 2, paper pH 6.5 to 7 and conductivity186.5 us/cm; and wash 3 pH (paper) 6.5 to 7, conductivity 38.2 us/cm. Itshould be noted that washes 1 and 2 were performed by letting themixture settle and then decanting the supernatant to waste. After wash3, the solid was collected via vacuum filtration through a 0.2 micronpore size nylon filter. The solid was dried via vacuum on the filterapparatus between 6 to 12 hours to yield the final product.

Referring now to the carbon layer, carbon removes creatinine, uric acidor other organic molecules that still may be present in the solution.For example, the carbon layer removes creatinine. The amount ofcreatinine that needs to be removed by this cartridge is approximately0.5 g to about 3.0 g. Although the volume of carbon can comprise a widerange, preferably approximately 50 to about 200 grams of carbon is used.Preferably, the carbon will be of the type that has the ability toremove less than 30 grams of glucose from the peritoneal dialysissolution. Thus, such a carbon layer will not remove an excess amount ofglucose from the dialysis solution. Activated carbon sold under thedesignation LP-50 by Carbochem, Ardmore, Pa., has been found to functionsatisfactorily in this regard. Other carbons can be used. It is believedthat carbons that are coconut shell based having a particle size of20×50 will also work. It should be noted that the carbon layer can belocated as any of the layers in the resin bed, although in a preferredembodiment it is the last layer.

FIG. 5 illustrates an embodiment of the resin bed 34 of the presentinvention. The resin bed 34, in the illustrated embodiment includes fivelayers 60, 62, 63, 64, and 66. The first layer 60 is a zirconiumphosphate layer having a pH of approximately 2.5 to about 5 andcomprising approximately 160 grams. The second layer 62 is a layer ofurease comprising approximately 25-250 mg of urease-CLEC in 25 gmzirconium phosphate/zirconium oxide or 50-100 gm of urease which is notcrosslinked from other sources. The third layer 63 comprises zirconiumphosphate having a pH of approximately 7 to about 7.5; preferably thereare approximately 380 grams of zirconium phosphate. The fourth layer 64is approximately 50 to about 75 grams of zirconium oxide at a pH ofapproximately 5 to about 7.5. The last layer 66 comprises approximately50 to about 200 grams of carbon and in an embodiment, 130 grams.

In the resin bed 34 the first layer 60 is used to remove sodium, Ca, andMg. Also this layer 60 will adjust the pH of the solution facilitatingthe conversion of urea to ammonium by the urease, second layer 62. Thethird layer 63 removes the ammonium generated by the urease layer 62. Tothis end, the zirconium phosphate needs to have a pH of greater than orequal to 5; in the illustrated embodiment the pH is 7 to 7.5. The fourthlayer 64 of zirconium oxide removes the phosphate and adjusts the pH toapproximately 7.4. The size of the fourth layer 64 needs to be such soas to allow the pH of the solution that exists the resin bed 34 to beadjusted to the desired pH. The last layer 66 is the carbon layer thatremoves any remaining impurities including creatinine.

In CFPD it is required to remove anywhere from approximately 5 to about20 gm urea/day. Table 1 below provides the amount of resin required forthe various layers in order to remove 5, 10, and 20 gm of urea.

For example, removal of 10 gm of urea generates 342 mmol of ammonia and171 mmol of bicarbonate. Using the resin bed of FIG. 4 to remove 342mmol of ammonia, a 380 gm layer of zirconium phosphate (resin pH=6.2,ammonia capacity=0.9 mmol/gm resin) was found to be necessary. In theprocess of removing the 342 mmol of ammonia the resin will release 342mmol of sodium into the solution. Zirconium phosphate at pH of 6.2 has acapacity of 0.63 mmol/gm resin for sodium and hence will re-adsorb342-127 mmol of sodium. As a result, an additional 127 mmol of sodiumneeds to be removed from the solution after passing through layer 63.Layer 60, which is also made up of zirconium phosphate removes thisamount of sodium. The amount of zirconium phosphate required to removethis amount of sodium varies as a function of pH of the resin. Table 3shows the amount of zirconium phosphate at various pHs required toremove 127 mmol of sodium. The amount of zirconium phosphate at variouspHs required to remove sodium is equal to:

sodium capacity (mmol/gm resin)=7.1−1.945 (pH of ZP) and 0.138 (H ofZp)².

Accordingly, at a pH of 2.5, the sodium capacity is 3.1 mmol/gm ZP. FromTable 3, at a pH of 7.2, to remove 171 mmol of sodium we need 53.4 gm ofzirconium phosphate.

The size of the zirconium oxide layer is controlled by the amountrequired to raise the pH from 6.2 to neutral during the entire therapytime. This amount is easily obtained from the pH profile curve. A gramof zirconium oxide resin has the capacity to raise the pH ofapproximately 0.45 L of solution from 6.2 to neutral. In an embodimentof a dialysis method it is necessary to process 48 L of the solution in8 hr, resulting in a requirement of 106 gm of resin. The amount ofzirconium oxide resin required to remove all of the phosphate in thesolution was found to be in the range of 60-80 gm. Thus the 106 gm ofzirconium oxide required to adjust the pH will also meet the requirementfor the removal of phosphate.

TABLE 3 Amount of Resin for 5, 10, 20 gm Urea Removed ZP Ammonia to ZPSodium to ZP layer size ZO Layer 3 be removed Layer 3 be removed atvarious pHs (gm) Layer 4 PH mmol size (gm) (mmol) 2.5 4.0 5.0 size(gm)7.2 171 285 171  53.4 114 190 60-80  6.2 171 285 — — — — 80-100 7.2 342380 342 107 228 380 60-80  6.2 342 380 127  40  85 141 106 7.2 684 456684 213 456 760 80-100 6.2 684 456  396.7 124 264 441 130

Referring now to FIG. 6 another embodiment of the resin bed of thepresent invention is illustrated. The resin bed 70 includes a five layerstructure. The layers are similar to the resin bed 34 of FIG. 4. In thisregard, the first layer 72 is zirconium phosphate, the second layer 74is urease, the third layer 76 is zirconium phosphate, the fourth layer78 is zirconium oxide, and the fifth layer 80 is carbon.

However, the first 72, third 76, and fourth 78 layers are slightlydifferent than their counterparts in FIG. 4. In this regard, the firstlayer 72 of zirconium phosphate preferably comprises 65 grams having apH of approximately 2.5 to about 5. The third layer of zirconiumphosphate has a pH of greater than 5 and in a preferred embodiment 6.2.This layer also comprises, as in the embodiment of FIG. 4, 380 grams.The fourth layer of zirconium oxide comprises approximately 130 gramsand has a pH of approximately 6.8 to about 7.5.

In the resin bed 70, once again, the first layer 72 removes the sodiumbut does not remove the ammonium. The first layer 72 will also adjustthe pH of the solution for converting urea to ammonium by the ureaselayer. The pH of the solution coming out of the first layer 72 will beapproximately the pH of the resin. The lower the pH of the resin, themore sodium is removed. As the solution exits the urease layer 74 andenters the third layer 76 of zirconium phosphate, the ammonium isremoved. As the pH of the zirconium phosphate is increased, moreammonium is removed. A pH of at least 5 is required in order to removethe ammonium. Once again, the fourth layer 74 of zirconium oxide removesthe phosphate and adjusts the pH to 7.4. The last layer 80, the carbonlayer, once again removes any remaining impurities.

Referring now to FIG. 7, a further embodiment of a resin bed 82 isillustrated. In this embodiment, the first layer 84 comprises urease.The second layer 86, in an embodiment, comprises zirconium oxide at a pHof approximately 9.5 to about 12.5. Preferably 100 to 150 grams ofzirconium oxide are present. The third layer 88 comprises zirconiumphosphate at a pH of approximately 6.2 to about 6.5. Approximately 680grams are present. The fourth layer 90 comprises zirconium oxide at a pHof approximately 6.8 to about 7.5 with preferably approximately 30 gramsbeing present. The last layer 92 comprises carbon.

In the resin bed 82 the zirconium oxide layer 86 functions in the roleof zirconium phosphate in the other resin beds (34 and 70). To this end,it removes the sodium. The amount of sodium removed is based on thecapacity of the zirconium oxide to remove sodium. The zirconium oxidefunctions to remove sodium due to its high pH. On the other hand, one ofthe disadvantages of this structure as compared to the other resin beds(30 and 70) is that a high pH is required so that as the solution exitsthe second layer 86 it is at a higher pH.

Generally, it should be noted that preferably the resin beds of thepresent invention are structured so that urea is removed in either thefirst or second layers. Then preferably sodium is removed. After thesodium is removed, ammonium and then phosphate is removed. Additionally,the zirconium oxide layer functions to control the pH of the solutionexiting the resin bed.

As previously noted, the resin bed of the cartridge can comprise anynumber of layers greater than four. It should also be noted that thelayers may not have discrete boundaries, but, may be blended together.For example, it is possible to have a gradient of two materials betweenthe zirconium oxide and the zirconium phosphate layers.

By way of example, and not limitation, real-time values for soluteconcentration at the inlet and outlet of cartridge 32 of the presentinvention will now be set forth. Due to mixing and mass transfereffects, these concentrations will be different at other locations ofthe system.

Parameter Input value Output value Urea Concentration [mg/L]  5-20 <10%of input value Creatinine concentration [ ] 2   <20% of input valuePhosphate concentration [ ] <20% of input value Sodium concentration[mEq/L] 122-142 122-142 Calcium concentration [mEq/L] 2.5 <0.2 Magnesiumconcentration [mEq/L] 0.5 <0.05 Ammonium concentration [ppm] n.a. <20Aluminum concentration [ppb] n.a. <10

Average Values

Preferably, the time-averaged concentration of the following parameterswill be maintained within the given boundaries as measured in thecartridge effluent:

PH 7.0-7.4 Sodium [mEq/L] 127-137 Chloride [mEq/L] 85-98 Bicarbonate[mEq/L] 25-35

The pH of the effluent from the cartridge will be maintained between 6.5and 8.0 at all times

Net Solute Removal/Addition

Parameter Amount Removed Urea-nitrogen 9.8 at an input concentration of20 mg/dL Creatinine 1.44 g Phosphate 1.44 g Sodium 20-60 mEq Bicarbonate20-60 mEq

Note: The capacity to process urea, creatinine, or phosphate dependsupon the input concentration of that component. The capacity for a givencomponent is defined by the component breakthrough, which is the amountabsorbed by the cartridge when the effluent concentration exceeds aprescribed level (i.e., 10% of the input value). For safety reasons,Ammonium breakthrough levels are defined in absolute terms at 20 ppm.

As noted above, a variety of different layer structures for the resinbed are possible within the cartridge 32. In constructing the cartridge32, the processes occurring in the cartridge must be considered. Whilethe cartridge performs its primary task of removing urea, creatinine,phosphate, and other toxins, the by-products of this process result inchanges in dialysate composition in three important respects: 1) sodium;2) pH; and 3) bicarbonate. These three parameters are intimatelyrelated.

Sodium can be affected by three distinct processes within the cartridge:

1) Release of sodium in exchange for ammonium and other cations(calcium, magnesium, potassium). The maximum quantity of these cationsto be absorbed will be about 650 mmol, consisting of about 430 mmol ofammonium and about 200 mmol of the other cations. The amount of sodiumreleased during this exchange process is dependent on the equilibratedpH of the zirconium phosphate, the solution pH, and the concentration ofcations in the dialysate.

2) pH equilibration of zirconium phosphate. In this process, sodium isexchanged for hydrogen ion in response to a solution pH which isdifferent from the equilibrated pH of the resin. This exchange can occurin either direction, depending on whether the solution pH is above orbelow the equilibrated pH. It is expected that the solution pH will begreater than the equilibrated pH of the resin for much of the therapy,resulting in a net adsorption of Na⁺ from solution.

3) Ion exchange of zirconium oxide. As an amphoteric resin, zirconiumoxide is capable of removing sodium from solution if the equilibrium pHof the zirconium oxide is sufficiently basic.

4) Adsorption of sodium by the mixed bed (demineralization) resin, ifpresent. The amount of sodium absorbed is entirely dependent on thequantity of mixed bed resin present.

5) Liberation of alkali upon conversion of urea. Conversion of urea is acontinuous process throughout the therapy. Conversion of urea maycontribute up to 430 mmol alkali, and is directly related to a patient'surea load.

6) Formation of bicarbonate during the conversion of urea. Formation ofbicarbonate acidifies the solution, but this effect is partially offsetby venting of carbon dioxide from solutions.

7) Venting of carbon dioxide from the cartridge loop. In solution,carbon dioxide acts as an acid. Thus, removal of carbon dioxide by itsmovement to the gas phase and subsequent venting out of the systemresults in a net loss of acid from solution.

8) Buffering of the solution by zirconium phosphate. It is expected thatthe solution pH will be greater than the equilibrated pH of the resinresulting in a net release of acid (H⁺) to the solution.

9) Buffering of the solution by zirconium oxide. The zirconium oxideresin exchanges H⁺/OH⁻ if it is in contact with a solution having a pHdifferent from its equilibrated pH.

Bicarbonate levels can be affected by three distinct processes withinthe cartridge:

1) Formation of bicarbonate during the conversion of urea. One mole ofcarbon dioxide/bicarbonate is formed from each mole of urea. Dissolvedcarbon dioxide is in equilibrium with bicarbonate according to thefollowing relation:

${pH} = {6.2 + {\log \frac{{HCO}^{3 -}}{{CO}_{2}({aq})}}}$

Consequently, the ratio of carbon dioxide/bicarbonate formed as a resultof the urease reaction is dependent on the solution pH, with more acidicconditions favoring carbon dioxide. The overall quantity of (carbondioxide+bicarbonate) formed is dependent on the patient's urea load.

2) Venting of CO₂ from the cartridge loop. Dissolved carbon dioxide isin equilibrium with the partial pressure of carbon dioxide in the gasphase. Thus, carbon dioxide will bubble out of solution if the solutionpartial pressure exceeds the partial pressure of the gas phase.

3) Adsorption of bicarbonate by zirconium oxide zirconium oxide resin inthe hydroxyl form is capable of adsorbing bicarbonate. Conversely,zirconium oxide resin in the bicarbonate form is capable of releasingbicarbonate into the solution.

The possible manipulations within the cartridge that can be made are asfollows:

1) Altering the equilibrated pH of the zirconium phosphate resin. Bylowering the equilibrated pH of the resin, the amount of sodium releasedis reduced, the average dialysate pH is lower, and the amount of carbondioxide formed is greater. By raising the equilibrated pH of the resin,the solution pH becomes more physiologic, but the amount of sodium andbicarbonate released is increased.

2) Altering the equilibrated pH of the zirconium oxide resin or loadingthe resin with various counter-ions. Hydroxyl-loaded zirconium oxideresults in a more physiologic solution pH, adsorption of bicarbonatefrom solution and increased adsorption of cations.

By way of example and not limitation, the experiments below set forthfurther embodiments and analysis of the invention.

Experiment No. 1

Set forth below are tests that examined the effect of modifying theequilibrium pH of zirconium phosphate on the composition of thedialysate effluent. The primary endpoints observed were pH, sodiumconcentration, and bicarbonate concentration. The ideal result is aneffluent pH at or near the physiologic pH of 7.4, a net sodium removalof ˜50 mEq for a full-sized cartridge, and a net bicarbonate addition of˜50 mEq for a full-size cartridge. These experiments were typicallyconducted at a g scale of zirconium phosphate, in a manner such that theurea concentration at ammonium breakthrough is in the expected columninput range during patient therapy. At this scale, appropriateperformance targets are a net sodium removal of ˜1 mEq and a netbicarbonate addition of 1 mEq (or 0.5 mEq/L for a 2 liter reservoir).

The resin was modified with phosphate buffer to increase the effluent pHby the following procedure. A large reservoir of 15 mM phosphate bufferwas prepared using 10.8 mM dibasic sodium phosphate, 4.2 mM of monobasicsodium phosphate and 117 mM sodium chloride. The buffer was pumpedthrough a column of resin in single pass mode. The flow rate was scaledto achieve a residence time of 5 minutes. The effluent pH was monitoredclosely, and the experiment was stopped when the effluent pH reached thedesired value.

With this technique the action can be modified up to a pH of 7.2. Forhigher pH the same phosphate buffer is prepared and 0.1 M NaOH is addedto raise the pH to the desired value.

For the modified zirconium phosphate materials, static tests wereperformed to determine the equilibrium capacity for ammonium. Theequilibrium isotherms for the different materials are not significantlydifferent from one another over the working concentration range [3-15mM].

Tests were performed using a 2-liter bag as a reservoir withrecirculation through columns containing the material. The bag wasmaintained at a uniform concentration with the aid of a shaker. Thesolution was pumped through the column(s) and returned to the solutionbag. The bag has an outlet port with an injection site, and an inletport that is extended 9.5 inches into the bag. The extension of theinlet port into the bag minimizes channeling between the two ports andensures proper mixing. The solution used in these tests was Dianeal PD4(1.5% glucose) spiked with urea and bicarbonate precautions were takenduring the filling and sampling procedures to ensure that the integrityof the system was maintained.

All the tests were performed using a urea concentration of 10 mg/dL anda sodium bicarbonate concentration of 25 mM. The initial pH for thissolution was 7.4.+−.0.2. For all the tests, 10 grams of cation materialwere used. Two types of urease were employed in these tests, CLEC-ureasefrom Altus Biologics (5-20 mg) and urease from Sorb Technologies (5 gmixed with 10 g alumina). For the Sorb urease a 25 mL column was usedwith 8 μm filters on both ends. The urease alumina mixture wassandwiched between two lays of alumina (˜5 g each). The Sorbtech ureasewas packed dry. The CLEC-urease was packed wet, sandwiched betweenlayers of Sephacryl (inert chromatography media from Sigma Chemicals) ina 10 ml column. No difference in performance was observed between thetwo forms of urease.

Prior to the experiment the urease was flushed with Dianeal to removeany labile or very small particle size enzyme. After the pump wasstarted, time zero was defined by the appearance of fluid exiting thecolumn outlet port. Samples were collected over time from both the inletand outlet to the two-liter bag, and analyzed immediately for sodium, pHand bicarbonate using a blood gas analyzer (Chiron model 860, ChibaCorning).

Table 4 shows a summary of the relevant tests performed. Additionalexperiments were performed using a phosphate buffer.

From these tests it is apparent that the change in pH during the test isreduced when the pH of the resin is modified to a higher (than 6.2) pH.With an increase in resin pH the performance of the resin in terms ofammonia adsorption maintains the same, but more sodium is released intothe system. The presence of the urease works in reducing the changes inpH.

TABLE 4 Results of small-scale test using urease and zirconium phosphateSolution Solution NH4⁺ Resin pH, pH, ΔNa ⁺ bound ΔHCO3 pH Date initialfinal ΔpH (mEq) (mEq) (mmol/L) 6.2 Apr. 21, 2000 7.80 7.13 −0.67 0.5 7.30.5 6.8 May 4, 2000 7.41 7.21 −0.20 3.8 8.6 2.5 7.1 Apr. 21, 2000 7.257.47 +0.22 5.5 5.9 4.4 7.4 May 4, 2000 7.45 7.59 +0.14 5.1 6.5 2.9 7.4May 15, 2000 7.38 7.46 +0.08 4.9 6.9 1.7 7.6 May 6, 2000 7.44 7.47 +0.035.5 8.8 5.3 7.6 May 15, 2000 7.36 7.56 +0.20 4.1 7.3 3.2

Experiment No. 2

Experiments were conducted using urease, zirconium phosphate, andzirconium oxide in the same experimental set-up as above. Multiplecolumns were connected in series, with the zirconium oxide column addedto the system after the cation column. The results for a test usingAltus 271-6 urease, zirconium phosphate modified to a pH of 7.2 andzirconium oxide are set forth below in FIGS. 8-10. Note that the sodiumbalance is well maintained over the course of the test, which is aresult of zirconium oxide removing sodium from the solution tocounterbalance sodium released by the zirconium phosphate layer.Effluent pCO₂ levels are also significantly lower in the presence ofzirconium oxide. Modified zirconium oxide captures sodium, and helpsmaintain the sodium balance over the course of the test. The test showthat zirconium phosphate modified to a pH of 7.1-7.2 performs muchbetter than those modified to a higher pH.

Experiment No. 3

Experimental Setup:

FIG. 11 illustrates a schematic of the experimental setup used in astudy to evaluate the use of ion exchange resins in peritoneal dialysissetting. The set up included two loops 100 and 102. A 15-liter bag 104representing the total fluid body of a patient was used in the secondloop 102 of the setup. Although utilizing a 40-liter bag may make a moreaccurate estimation of the patient body, a 15-liter bag was used due toease of analysis. The fluid from the 15-liter bag was pumped into thelumen side 106 of the dialyzer 108 at a flow rate of 100 mL/min using apump 110. From the outlet 112 of the lumen side 106 of the dialyzer 108,the fluid returned to the 15-liter bag 104. Concurrently, as this fluidwas returning into the 15-liter bag 104, it was infused with urea,creatinine, and phosphate, at 1 mL/min, to represent the total amount ofwastes being generated continuously by the patient. The 15-liter bag 102was maintained at a constant concentration of urea-nitrogen (20 mg/dL),creatinine (6 mg/dL), and phosphate (3.1 mg/dL). The initial feedsolution contains 25 mmol/L of bicarbonate, 138 mEq/L of sodium, 2.5mEq/L of calcium and 1.0 mEq/L of magnesium.

A 4-liter bag 114 containing sodium at 132 mEq/L, calcium at 2.5 mEq/L,magnesium at 1.0 mEq/L and bicarbonate at 25 mmol/L in DI water isprovided. Initially the 4-liter solution is used to prime the dialyzer108 and a cartridge 116. As the solution exits the cartridge 116, allthe toxins and also calcium and magnesium, are completely removed.Accordingly, fluid returning to the 4-liter bag 114, is infused withcalcium and magnesium so as to maintain the calcium and magnesiumbalance in the 15-liter bag 114. Both the 4-liter 124 and the 15-liter114 bag were well mixed and the dialyzer 118 was operated at close tozero ultra filtration.

From the 4 L bag 114, the solution flows into the shell side 128 of thedialyzer 108. The urea creatinine and phosphate diffuses from the lumenside 116 of the dialyzer 108 to the shell side 128. The solution thatexits the dialyzer 108 and enters the cartridge 116 has a urea nitrogenconcentration of 10 mg/dL, Creatinine concentration of 3 mg/dL andphosphate 1 mg/dL. The flowrate on either side of the dialyzer 38 ismaintained at 100 ml/mm.

The cartridge 116 was constructed as set forth above. Urea creatinineand phosphate flows to the bottom 130 of the cartridge 116, whichcontains urease, various ion exchange resins, and carbon. As notedabove, urease is an enzyme whose function is to convert toxic urea intoammonium and carbon dioxide, is the first layer in the cartridge. Themiddle layer comprises of two different types of ion exchange resins,zirconium phosphate (zirconium phosphate) and zirconium oxide (zirconiumoxide). Zirconium phosphate, as noted above, mainly removes ammoniumions, calcium, and magnesium from the solution, while releasing hydrogenand sodium. The zirconium oxide resin removes the phosphate. Finally, acarbon layer is used to remove creatinine, uric acid, and other organicsfrom the solution. From the top of the cartridge, fluid is then directedback into the original 4-liter bag 114.

Pursuant to this study, samples were taken at 5 different points in theabove setup. Sample “1” (C_(IN)) was taken before the fluid enters thecartridge inlet; Sample “2” (C_(OUT)) was taken as the sample exitsafter the cartridge; Sample “3” (4 L) was taken directly from theoutflow of the 4-liter bag; Sample “4” (D_(OUT)) was taken as the fluidcomes out of the lumen of the dialyzer; Sample “5” (D_(IN)) representsthe fluid before entering the lumen inlet of the dialyzer. The sampleD_(IN) was taken from the 15 L bag 34, which is essentially well mixedand represents 15 L patient.

The above experimental setup was used to evaluate an embodiment of thecartridge of the present invention. A Redy Cartridge was obtained fromSorb Technology and used in the above experimental setup. FIG. 12 showsthe various layers in the cartridge. FIG. 12 a represents the RedyCartridge, FIG. 12 b represents the Redy Cartridge 1 and FIG. 12 crepresents the Redy Cartridge 2. The urea, creatinine and phosphatediffuse from 15 L patient bag across the dialyzer to the bottom of thecartridge. Five samples were taken from various locations as shown inFIG. 11. Samples were analyzed for pH, bicarbonate and sodium onsite.Analysis for urea, creatinine, phosphate, calcium, magnesium, chloride,lactate, and glucose were also carried out. FIGS. 13 a, 13 b, 13 c showthe pH, sodium and bicarbonate profiles. The pH in the 15 L patient bathdrops from 7.546 to 6.156, bicarbonate drops from 23.2 to 0.0, sodiumincreases from 132.4 mEq to 135.3 mEq.

Instead of providing bicarbonate to the patient, bicarbonate is removedand sodium added. Also the pH drops and PCO2 increases. Table 4summarizes the pH, sodium, and bicarbonate profile from this study.Overall, 44 mEq of sodium was added and all of the bicarbonate wasremoved. This was a net gain of 125 mEq of sodium. The cartridge doesremove urea, creatinine and phosphate completely, but does not satisfythe electrolyte requirement. Thus the resins or the cartridge cannot beused in peritoneal dialysis closed loop setting or in hemodialysisapplications, it cannot be used unattended. Several differentcombinations were evaluated that could satisfy the requirement criteriafor use in the cartridge for continuous recirculation of peritonealdialysis solution. Some of the combinations were as follows:

1—Zirconium oxide in bicarbonate form at a pH of 8.85 used withzirconium phosphate (pH=6.2) in its standard form. In this setup therewere only 4 layers.

2—Zirconium phosphate with a pH of 6.5 along with zirconium oxide in thebicarbonate form at two different pHs of 10.52 and 7.33. At the higherpH, bicarbonate should be in the form of carbonate.

3—Zirconium phosphate at a pH of 6.5 was used the bicarbonate form ofzirconium oxide at a pH of 9.35 and 9.83 and the hydroxyl form of thezirconium oxide at a pH of 7.14 and 7.23.

4—Zirconium phosphate at a pH of 6.49 used along with zirconium oxide inthe bicarbonate form at a pH of 8.80. In this case also there were 4layers.

5—Since zirconium oxide is an amphoteric resin, this resin needs toadsorb the Ca⁺⁺ and Mg⁺⁺ ions, allowing the reduction of zirconiumphosphate volume to 450 ml.

FIGS. 12 b and 12 c represents two alternatives from the variousalternatives discussed.

FIG. 12 b and FIG. 12 c shows the modified cartridge in the study. Fromequilibrium adsorption isotherm studies it was shown that at aconcentration of 10 mg/dl urea nitrogen in the peritoneal dialysissolution a 600 ml resin column is required. Therefore the size of theresin in Cartridge I (FIG. 6 b) is 600 ml. In FIG. 2 b, (cartridge I)the 1^(st) layer is urease, 2^(nd) layer is zirconium phosphate (pH=6.5,volume=200 mL), 3^(rd) layer is zirconium oxide in carbonate form(pH=9.48, volume=100 mL), 4^(th) layer is zirconium phosphate (pH=6.5,volume=400 mL) and 5^(th) layer is Zirconium oxide in the hydroxyl form(pH=7.38, volume=30 mL) the last layer is carbon. The zirconium oxide3^(rd) (High pH) is used not only to adsorb the cations, but it can alsoraise the pH of the zirconium phosphate resin. The counter ions used inthis resin could be bicarbonate, carbonate or hydroxyl. This layeradsorbs the calcium, magnesium, thus reducing the size of the zirconiumphosphate layer as it is used only to adsorb ammonia. Phosphate is alsoadsorbed in this layer along with the other cations. The 5^(th) layer iszirconium oxide (pH=7.38) is used to adsorb phosphate and some sodium.But if there is no leaching of phosphate from the zirconium phosphateresin, this layer will not be required. The last layer is carbon, whichagain, can be placed anywhere.

FIGS. 14 a, 14 b & 14 c represent the pH, sodium bicarbonate and profileover the entire therapy time. Table 5 summarizes the pH, bicarbonate andsodium profile. The pH in the 15-liter patient bag goes from 7.49 to6.9. Sodium is removed from the patient (15-liter bag) approximately 57mEq is removed. The resins are designed such that it removes sodiuminitially for approximately 20 minutes or so, and then the cartridgeslowly adds the sodium back. Similar trend is observed in the case ofbicarbonate, also approximately 22.5 mEq of bicarbonate is added back tothe 15-liter patient. In this experiment, as shown in FIG. 14 d 4.94 gmof urea nitrogen is processed (10.6 gm of urea) which produces 353mmol/L of ammonia and 176 mmol of bicarbonate. In the Redy cartridge run124 mEq of sodium was added, but in our cartridge of the presentinvention only 5 mEq of sodium is added back into the circulation. Inthe cartridge of the present invention, the net bicarbonate gain wasapproximately 59 mEq. But in the cartridge run bicarbonate wascompletely removed. The pH in the 15-liter patient loop went down to6.15 and all the bicarbonate was removed.

FIG. 12 c shows the cartridge II used in the experimental setupdescribed in FIG. 10. The amount of zirconium phosphate was reduced to450 ml. Layers 2 and 4 were zirconium oxide in carbonate and bicarbonateform at pH of 10.52 and 7.33. Table 6 summarizes the results from thisrun. In this run, the pH of the zirconium oxide in layer 2 was higher sothat it has better capacity for cations. Around 97.5 mEq of sodium wasremoved from the 15-liter patient bag and 15 mEq of bicarbonate wasremoved. There was net removal of 62 mEq of sodium. An addition of 5 mEqof bicarbonate in the stream. The bicarbonate profile can be improved inthis run. Here we have also reduced the amount of zirconium phosphate toremove the same amount of urea.

FIGS. 15 a, 15 b and 15 c shows the pH bicarbonate and sodium profileover the entire therapy time. FIG. 15 d shows the urea conversion. Inthis experiment a higher pH of the bicarbonate resin was utilized andalso the zirconium phosphate resin was only 450 ml.

TABLE 5 Summary of Cartridge Test Gain/Loss Gain/Loss Cartidge 4-literBag 15-Liter 15-Liter Bag Time (Min.) In Out 4-Liter Bag (mEq) In Out(mEq) 0 pH — — 7.147 — 7.546 — — 480 pH   6.153  6.3 6.17 — 6.14 — 6.1560 Sodium — — — — 132.4 — — (mEq/L) 480 Sodium 137.3 166.3 141.7 81.2135.3 139.3 43.5   (mEq/L) 0 Bicarbonate — — 23.2 — 23.1 — — (mEq/L) 480Bicarbonate — — — — 10 — — (mEq/L)

TABLE 6 Summary Cartridge 1 Gain/Loss Gain/Loss Cartidge 4-liter Bag15-Liter 15-Liter Bag Time (Min.) In Out 4-Liter Bag (mEq) In Out (mEq)0 pH — — 6.99 — 7.49 — — 480 pH  6.9   7.09 7.06 — 6.9   6.997 — 0Sodium — — 124.4 — 137 — — (mEq/L) 480 Sodium 135.4 142.6 139.9 62 133.2 137.2 57  (mEq/L) 0 Bicarbonate — — 22 — 23.4 — — (mEq/L) 480Bicarbonate  28.4  31.8 31.1 36.4 24.9  26.4 22.5 (mEq/L)

TABLE 7 Summary Cartridge II Gain/Loss Gain/Loss Cartidge 4-liter Bag15-Liter 15-Liter Bag Time (Min.) In Out 4-Liter Bag (mEq) In Out (mEq)0 pH — — 7.08 — 7.42 — — 480 pH   7.106   7.235 7.2 — 7.036   7.122 — 0Sodium — — 126 — 136.60 — — (mEq/L) 480 Sodium 132.6 139.9 135.3 37.2130.1 133.7   99 (mEq/L) 0 Bicarbonate — — 22 — 23.5 — — (mEq/L) 480Bicarbonate  26.2 28  26.9 19.6 22.5 24  −15 (mEq/L)

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. A device for removing uremic toxins in a dialysis procedure, thedevice comprising: a body having an inlet and an outlet and defining aninterior, the interior including a layer comprising urease, a layercomprising zirconium oxide, a layer comprising zirconium phosphate, anda layer comprising carbon; and the device being so constructed andarranged so that a fluid entering the device contacts the zirconiumphosphate layer upon entering the device before contacting the ureaselayer.
 2. The device of claim 1 wherein the fluid flows through theurease layer before entering the layer of zirconium oxide.
 3. The deviceof claim 1 wherein the zirconium oxide has been modified by removing thenitrate ion.
 4. The device of claim 1 wherein the zirconium oxide is ina bicarbonate form.
 5. The device of claim 1 wherein the zirconium oxideis in a hydroxyl form.
 6. The device of claim 1 wherein the carbon layeris located in juxtaposition to the outlet.
 7. The device of claim 6wherein the fluid flows through the layer of zirconium oxide beforeentering the carbon layer.
 8. The device of claim 1 wherein thezirconium phosphate has a pH of approximately 2 to about
 8. 9. Thedevice of claim 1 wherein the zirconium oxide has a pH of approximately6 to about
 13. 10. The device of claim 1 further comprising a secondseparate layer comprising zirconium phosphate, the urease layerpositioned between the layer comprising zirconium phosphate and thesecond separate layer comprising zirconium phosphate.
 11. The device ofclaim 1 further comprising a second separate layer of zirconium oxide.12. The device of claim 1 including an open header at each of the inletand outlet end of the device.
 13. The device of claim 1 including anopening for venting a gas to the atmosphere located at the outlet end.14. A device for removing uremic toxins in a dialysis procedure, thedevice comprising: a body having an inlet and an outlet and defining aninterior, the interior including: a modified urease layer comprising amodified urease selected from the group consisting of cross-linkedenzyme crystals of urease, a blend of urease and zirconium oxide,alumina-stabilized urease and combinations thereof, a layer comprisingzirconium oxide, a layer comprising zirconium phosphate, and a layercomprising carbon; and the device being so constructed and arranged sothat a fluid entering the device contacts the zirconium phosphate layerupon entering the device before contacting the modified urease layer.15. The device of claim 14 wherein a fluid entering the device contactsthe zirconium phosphate layer upon entering the device before contactingthe zirconium oxide layer.
 16. The device of claim 14 wherein the bodyfurther comprises a rough interior surface, the rough interior surfacepreventing fluid flow along the interior surface.
 17. The device ofclaim 14 further comprising a second separate layer comprising zirconiumphosphate, the modified urease layer positioned between the layercomprising zirconium phosphate and the second separate layer comprisingzirconium phosphate.